This invention relates to the field of micro-electro-mechanical systems (MEMS), more particularly to micromechanical memory cells.
Static random access memory (RAM) is formed using a bistable circuit element, the cross-coupled latch. The cross-coupled latch typically is formed using six transistors. Each element of the static RAM holds one bit of information in the cross-coupled latch. Once the static RAM cell has been written to, the data is held without further action. A read operation from the static RAM is non-destructive, in that it does not deplete the stored data, and the data may be read from the static RAM multiple times.
A dynamic RAM uses only a single transistor to gate a charge on a capacitor. The state of the capacitor is read back through the same gate transistor. The capacitor can only store the charge, and therefore the information, for a limited time. Reading the state of the stored charge also depletes the charge. A dynamic RAM periodically must be refreshed to reinstate the charge on the capacitor. It is common practice to perform a rewrite operation after each read operation to ensure a sufficient charge remains stored on the capacitor. What is needed is a memory element that is bistable like the static RAM, yet composed of very few circuit elements like the dynamic RAM.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for a micromechanical memory element. One embodiment of the claimed invention provides a micromechanical memory element. The micromechanical memory element comprising: a pass transistor; a first member biased at a first member voltage; a second member biased at a second member voltage; a deflectable member between the first and second members, the deflectable member receiving an electrical signal from the pass transistor, the deflectable member operable to deflect toward the first member when the electrical signal is a first state, and toward the second member when the electrical signal is a second state; a first contact positioned to contact the deflectable member when the deflectable member is deflected toward the first member, the first contact providing a first contact voltage operable to hold the deflectable member in contact with the first contact in the absence of a signal from the pass transistor; and a second contact positioned to contact the deflectable member when the deflectable member is deflected toward the first member, the second contact providing a second contact voltage operable to hold the deflectable member in contact with the second contact in the absence of a signal from the pass transistor.
Another embodiment of the present invention provides a micromechanical memory element. The micromechanical memory element comprising: means for deflecting a deflectable member in one of two positions depending on a state of an input signal line; means for holding the deflectable member in the deflected state; and means for detecting the deflected state.
Another embodiment of the present invention provides a micromechanical memory element. The micromechanical memory element comprising: a pass transistor; a first member biased at a first member voltage; a deflectable member receiving an electrical signal from the pass transistor, the deflectable member operable to deflect toward the first member when the electrical signal is a first state; and a first contact positioned to contact the deflectable member when the deflectable member is deflected toward the first member, the first contact providing a first contact voltage operable to hold the deflectable member in contact with the first contact in the absence of a signal from the pass transistor.
Another embodiment of the present invention provides a method of forming a micromechanical memory element. The method comprising: providing a semiconductor substrate; forming addressing circuitry on the substrate; forming a first member and a first contact on the substrate, the first member and the first contact electrically connected to the addressing circuitry; forming a first sacrificial layer on the substrate; and forming a deflectable member on the first sacrificial layer, the deflectable member electrically connected to the substrate.
Another embodiment of the present invention provides a method of forming a micromechanical memory element. The method comprising: providing a semiconductor substrate; forming addressing circuitry on the substrate; forming a first member and a first contact on the substrate, the first member and the first contact electrically connected to the addressing circuitry; forming a first sacrificial layer on the substrate; forming a deflectable member on the first sacrificial layer, the deflectable member electrically connected to the substrate; forming a second sacrificial layer on the deflectable member; forming a second member and a second contact on the second sacrificial layer, the second member and the second contact electrically connected to the addressing circuitry; and removing the first and second sacrificial layers.
The disclosed micromechanical memory element may provide the stability of a conventional static RAM and the low component count of a conventional dynamic RAM.